The present disclosure relates to medical implant delivery systems and methods and, more particularly, to delivery systems and methods for positioning an expandable prosthetic heart valve in a patient's vasculature.
Prosthetic heart valves are usually implanted in the human heart to replace natural valves. These valves essentially function as check valves, permitting the blood to flow through the valves in a downstream direction, but blocking blood flow in a reverse or upstream direction. Some prosthetic heart valves include an annular valve housing or body with a central orifice and occluders. The orifice provides a passageway for the blood, and the occluders open and close to regulate the passage of blood. For instance, U.S. Pat. Nos. 5,876,436 and 6,719,790 describe in detail specific prosthetic heart valves. Both of these references are hereby incorporated herein by reference in their entireties.
One type of prosthetic heart valve is collapsible to a relatively small circumferential size. This type of prosthetic heart valve can be delivered into a patient less invasively than valves that are not collapsible. For example, a collapsible valve may be delivered into the patient via a tube-like delivery apparatus such as a catheter, a trocar, a laparoscopic instrument, or the like. This can avoid the need for a more invasive procedure such as full open-chest, open-heart surgery. When the collapsed valve has reached the desired implant site in the patient (e.g., at or near the annulus of the patient's heart valve that is to be effectively replaced by the prosthetic valve), the prosthetic valve can be expanded to full operating size and released from the delivery apparatus. Typically, in its full operating size, the prosthetic valve engages adjacent native tissue of the patient to firmly anchor itself in the patient.
Because valves of the type described above are basically implanted by remote control (because the valve is inside the patient at the far end of delivery apparatus that is manipulated and controlled from its proximal end outside the patient), it can be difficult to get the valve to exactly the right location in the patient before releasing it from the delivery apparatus. Improvements are therefore sought with respect to how such valves are deployed.
One percutaneous delivery method entails introducing a collapsible prosthetic heart valve through a patient's femoral artery. This delivery method is referred to as a transfemoral approach. In transfemoral valve implantation, the collapsible prosthetic heart valve is delivered in a retrograde manner from the femoral artery through the aortic arch to, for example, the native aortic valve annulus.
A delivery system and an introducer may be used to deliver the prosthetic heart valve to the native aortic valve annulus using the transfemoral approach. As seen in FIGS. 1 and 2, a conventional delivery system may include a distal sheath 30 for slidably enclosing a valve-containing compartment, and a proximal outer shaft 20 for controlling sliding movement of the distal sheath to open and close the compartment. The delivery system may further include a tip 32 having a maximum diameter that is substantially similar to the outer diameters of the distal sheath 30 and the proximal outer shaft 20. For example, in an 18F delivery system, the proximal outer shaft 20, the distal sheath 30, and the maximum diameter of the tip 32 are each about 18F. In such conventional delivery systems, the distal end 34 of the distal sheath 30 may be outwardly flared as a consequence of contacting the proximal surface of the tip 32. The flared distal end 34 of the distal sheath 30 may catch on body tissue as the delivery system is advanced in the patient's vasculature. For instance, the distal end 34 of the distal sheath 30 may catch on the aortic valve, the calcified aortic annulus, and/or lesions or calcified tissue in the aortic arch.
During transfemoral valve implantation, the distal sheath 30 of the delivery system is bent significantly to pass through the aortic arch A, which significantly biases the sheath toward the outside wall W of the aortic arch A, as illustrated in FIG. 3. Consequently, the flared distal end 34 of the distal sheath 30 may forcibly contact at least a portion of the outside wall W as the delivery system is advanced toward the native aortic valve annulus. The distal end 34 of the distal sheath 30 may also catch on calcified tissue C located on the outside wall W of the aortic arch A, as seen in FIG. 3. The contact between the distal sheath 30 and the outside wall W of the aortic arch A may cause various adverse effects on the patient. For instance, when the delivery system passes through the aortic arch A, the distal end 34 of the distal sheath 30 may damage the outside wall W of the aortic arch A, or may sever calcified tissue C, which may in turn cause an embolism. It is therefore desirable to minimize the contact between the distal sheath 30 and body tissue when advancing a delivery system using the transfemoral delivery approach.